TV Tokyo spokesman Hiroshi Uramato said that a later broadcast of the show scheduled for 30 other stations nationwide had been canceled, and that an investigation was under way.

"We are shocked to hear many children were taken to hospitals," Uramoto said. "We will investigate thoroughly, and consult with experts."

The show, based on characters from Nintendo's popular "Pocket Monsters" video game, is Japan's most highly-rated program in its 6:30 p.m. time slot. Tuesday's episode, "Computer Warrior Porigon," features characters fighting each other inside a computer.

TV Tokyo declined to comment on what part of the cartoon caused the seizures, but most of the children developed the symptoms about 20 minutes into the program.

News reports blamed a scene in the cartoon that featured an exploding "vaccine bomb" set off to destroy a computer virus, followed by five seconds of flashing red light in the eyes of "Pikachu," a rat-like creature that is the show's most popular character.

Some other children were stricken later, when watching excerpts from the scene in TV news reports on the earlier victims.

Dr. Yukio Fukuyama, a juvenile epilepsy expert, said that "television epilepsy" can be triggered by flashing, colorful lights. Though the phenomenon was observed before television, photosensitive epilepsy, as it is also called, has become far more common as TV has spread. The same symptoms have also been observed in children playing video games.

Fukiyama says parents should be made aware of the danger. "The networks should definitely think of issuing a health warning beforehand," he said.

Psychologist Rika Kayama, author of a book on video games and health, said that "there is the possibility of photosensitive epilepsy or group hysterics."

"The children must have been totally immersed in the program," Kayama said.

A Nintendo spokesman told Reuters that the only link between its games and the cartoons was the characters.

"We don't expect the incident will have any immediate impact on our business in the Christmas season, since the television program and game are different," the spokesman said. Nintendo's games carry a health warning.